View transmission system



June 14, 1932. v K ZWORYK|N l 1,863,363

VIEW TRANSMISSION SYSTEM Filed Nov. l, 1929 IMVEATOR Wad/mf Z wary/6W Y ATTORNEY Patented June 14, 1932 UNITED STATES PATENT OFFICE VLADIMIR K. ZWORYKIN, 0F SWISSVALE, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURNG COMPANY, A CORPORATION PENNSYL- v VANIA VIEW TRANSMISSON SYSTEM Application led November 1,1929. Serial No. 403,973.

My invention relates to view-transmission systems and it has particular relation to certain devices used in such systems and known, generally, as light-choppers.

A light-chopper, of the generic class to which my invention pertains, is disclosed and described in the patent to Branson, No. 1,687,489. Such device functions to break up the light, falling upon a picture or document being transmitted, into a plurality of pulses that are, theoretically, of equal intensity and duration. The light, therefore, that reaches a photoelectric cell, after reflection from the picture or document or after passing through a picture negative, in certain types of viewtransmitting systems, causes the output current from the said cell to be pulsating in character, the amplitude of the pulsations corresponding to the intensity of the reflected light.

For transmission over metallic circuits, the carrier-frequency can be fixed directly by the number of openings in the chopper disc that pass per second betweenthe light source and the document. For radio-transmission, the frequency given by the chopper is not, usually, sufficiently high for radiation but it may be utilized to modulate the output from an oscillation generator operating at radio frequency. In either. event, however,` the pulsating character of the'photo-cell output current is highly advantageous in that it renders such current readilyv amplifiable, in amplifiers of well-known types, before transmission.

Light choppers, of the type whereby each light pulse is determined by a single opening in a disc, or the like, have not, however, given entire satisfaction. I have discovered, by research and experiment, that the failure of such choppers may be principally attributed to the fact that it is substantially impossible to so punch, bore, slit or otherwise perforate the chopper disc that the openings have absolutely the same dimensions. The slightest variation in width of the successive o enings or of the unperforated material etween openings gives rise to detrimental harmonics in the output current from the photoelectric cell that result in imperfect reproduction of the picture or document at the receiving end of the system.

It is, accordingly, an object of'my invention to provide a light-chopper that shall be capable ofdividing light from a fixed source into successive impulses that are substantially equal in duration and intensity.

Another object of my invention is to provide a light-chopper the satisfactory operation of which is not dependentupon the accurate boring or punching of successive openings.

In a successful commercial embodiment of my invention, l attain the aforementioned objects by associating a light-chopper disc, provided with a plurality of radial slots, with a masking device having a plurality of openings therethrough that correspond, in dimensions and spacing, to the openings in the disc. Vhen, therefore, light from a fixed source is permitted to pass, simultaneously, through more than a single opening in the disc, the said disc, as it rotates in a plane parallel to the plane of the masking device, interrupts the light at a rate determined by the angular velocity of the disc and the circumferential space between successive openings.

Variations in the dimensions and spacing of the individual openings are, accordingly, ineffective to cause changes in the average intensity and durationk of the light pulses' and, since a relatively large amount of light is passed, the frequency of the pulses canbe made materially higher than with'similarv devices with which I am familiar, without` detrimentally reducing the amount of'light eventually reaching the photoelectric cell.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and itsmethod of operation, to-V gether with additional objects vand advantages thereof, will best be understood from the following description of a specific embodiment, when read in connection with the accompanying drawing, in which:

Figure l is a` view, partly diagrammatic, exemplifying the use of my improved lightchopper in a view-transmittingsystem,

Fig. 2 is a view, in elevation, of the lightchcppper and masking device, as seen from the s1 e;

Figs. 3 and 4 are sectional views of the light-chopper and masking device, taken along a line corresponding to the line III--III in Fig. 2, indicating the manner in which the several elements cooperate to constitute a light valve when the chopper disc is rotated.

The apparatus illustrated in Fig. 1 comprises a cylinder 1, mounted for rotation and axial advance, and adapted to carry a picture or document. A fixed light source 2 is provided, and the light therefrom is concentrated, by a` lens 3, upon an opening 4 in a diaphragm 5. The light, passing through the opening, is further concentrated by a lens system comprising a plurality of lenses 6 and 7 upon the surface of the cylinder 1.

rfhe 1enses 6 and 7 are carried within a tube 8 that is disposed coaxially of a parabolic mirror 10, the focus of which coincides with the focal point of the said lenses, and the diaphragm 5 closes the end of the tube nearest to thel light source.

A zone, only, of the paraboloid is used because the apex thereof, if it were complete, would lie beyond the surface of the picture or document carried by the cylinder, which is mechanically impossible. The edge of the mirror is disposed as close to the surface of the picture as it may be and still provide proper mechanical clearance.

The parabolic mirror joins a plane lnirror 11 placed at an angle of substantially 45O to the axis ofthe paraboloid. An opening is provided in the central part of the plane mirror to accommodate the tube V8 carrying the diaphragm 5 and the lenses 6 and 7. The plane mirror and the parabolic mirror together constitute a chamber that opens into the interior of a housing 12 in which is dispoSed a photoelectric cell 13. The cell is protected, by the housing, from all light except that reected by the mirrors 10 and 11.

An amplifier 14 is usually provided by means of which the current pulses from the photoelectric cell are sufficiently amplified for direct transmission over metallic'circuits or for further use in the modulation of the carrier-wave of a radio-transmitting station.

A rotatable disc 15, provided with a plurality of radial openings 16, is interposed between the lens 3, nearest the light-source 2, and the diaphragm 5. The disc is so disposed, with respect to the beam of light, that a plurality of the openings are, simultaneously illuminated.

A fixed masking device 17, provided with a plurality of radial openings 18, corresponding, in dimensions and spacing, to the openings 16 in the disc, is mounted, in Yparallel relation to the disc, between the said disc and the light source.

A motor (not shown) is provided for applying a constant torque to the disc.

In the operation of my improved lightchopper the openings through the disc pass into and out of registry with the openings in the masking device as the disc is rotated, thus allowing the pencils of light that pass through a plurality of the said openings to be simultaneously utilized in the illumination of the diaphragm 5. Variations in the dimensions and spacing of the individual illuminated openings are, accordingly, averaged for each light pulse and the successive light pulses falling upon the picture or message, carried by the cylinder, are substantially equal to each other in duration and intensity.

The output current from the photoelectric cell, therefore, does not comprise a component corresponding to Veach inaccurately bored or punched opening in the chopper ldisc, and the reproduction of the picture, at the receiving end of the system, is greatly improved. Y

Although I have shown and described a specific embodiment of myinvention, I am fully aware that many modifications thereof are possible and that such modifications will be apparent to those skilled in the art.v My invention, therefore, is not to be limited except in so'far as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. Ina light-chopper, a rotatable disc provided with a plurality of openings therethrough and a fixed element, having similar openings, Vdisposed adjacent and parallel thereto.

V 2. In a lightvchopper, a. rotatable disc provided with a plurality of radial openings therethrough and a y fixed masking device, having similar openings, disposed adjacent and'parallel thereto.y

In testimony whereof, I have hereunto subscribed my name this 26th day of October,

i VLADIMIR K. ZWORYKIN. 

